Again you are judging by today's standards, Morrill Tariff was enough of a catalyst back then. Back then people took their states rights seriously.
To show how far we have strayed, how bass ackward everything is take the following test.
Most people couldn't answer the most basic questions about their state legislatures without looking it up on google. Can you answer these simple questions regarding your state legislature(without the aid of a search engine)?
But not the catalyst for Southern secession. When Francis Pickens was inaugurated governor of South Carolina, his inauguration speech spoke of ending the ties with the U.S. and gave no other reason than Lincoln's opposition to slavery. South Carolina started the whole secession ball rolling. And without slavery they wouldn't have taken that first step.